Compile fn from expr containing unbound symbols

partial_eval.clj

(ns expr-fn.core
  (:require [clojure.walk :as walk]))

(defn forms-seq [form]
  (tree-seq coll?
            #(if (map? %) (interleave (keys %) (vals %)) %)
            form))

(defn resolved? [form]
  (if (coll? form)
    (every? resolved? form)
    (not (symbol? form))))

(defmacro partial-eval [expr env]
  (let [args (->> expr forms-seq (filter symbol?) (remove env) vec)
        body (->> expr
               (walk/prewalk-replace env)
               (walk/prewalk #(if (and (seq? %) (resolved? %))
                                (apply (first %) (rest %))
                                %)))]
    `(fn ~args ~body)))